Process and apparatus for lapping gears and other objects



Sep&. 11, 1928. 555,869

A. W. COPLAND PROCESS AND APPARATUS FOR LAPPING GEARS AND OTHER OBJECTS Filed Feb. 26, 1926 4 Sheets-Sheet 1 ATTGQA/EK Sept. '11, 1928. 1,683,869

A. w. COPLAND PROCESS AND APPARATUS FOR LAPPING GEARS AND OTHER OBJECTS Filed Feb. 26, 1926 4 Sheets-Sheet 2 60 illlllllllllll Ar/am B Sept. 11, 1928. A 1,683,869

A. V\!. COPLAND PROCESS AND APPARATUS FOR LAPPING GEARS AND OTHER OBJECTS Filed Feb. 26, 1926 4 Sheets-Sheet 3 I 2 I I 3 .52 5/ I )1 A" 1 l 52 w n WW. I M 1 49 1, Max 50 50 g 4; W L W u; g a

Arramw-v Sept. 11, 1928. 1,683,536?

A. W. COPLAND PROCESS AND APPARATUS FOR LAPPING GEARS AND OTHER OBJECTS Filed Feb. 26, 1926 4 Sheets-Sheet 4 A Tram'vEK Patented Sept. 11, 1928.

.ALEXANDER W.. COIBLAND, OF BIRMINGHAM,

TRUST COMPANY, OF DETROIT, MIGHIGALL.

MICHIGAN, ASSIGNOR TO. DETROIT A. CORPORATION OF MICHIGAN.

PROCESS AND APPARATUS FOR LAPPING GEARS AND OTHER OBJECTS.

Application filed February 26, 1926. Serial No. 90,949.

The invention relates to the finishing of gears and various other objects by a peculiar and novel form of lapping operation.

One of the objects of the invention is the i. provision of an improved method of lapping that is capable of finishing the teeth of gears or other more or less similarly toothed bodies with a high degree of accuracy and, that is applicable to bevel gears of both plane and 1e spiral forms.-

Another object of the invention is the provision of a method of lapping the teeth of peripherally toothed bodies of rotation, including gears, splined shafts and the like, in which the relative movement of the la and body are on lines substantially para lel tothe rotation axis of the body and which method is applicable to toothed bodies such as referred to having their inner-tooth or inter-spline spaces closed or interrupted by surfaces transverse to the said axis of rotation. A further provision of an improved process of lapping which is applicable to the finishing of a great variety of irregularly formed bodies.

Another object of the invention is the pro vision of an improved form of lapping apparatus and particularly apparatus that is adapted to the carrying out of processes such as referred to above.

Other objects more or lessincidental or anci l lary to the foregoing will be apparent from the description which follows.

In carrying out my process of lapping I first form a lap with surfaces complementary to the surfaces of the objectto be lapped.

The lapcan be formed in various ways. For example, it can be formed by casting suitable to material against the surface of the object to be lapped or against asimilarly formed mold surface. Or the lap can be formed by machining or it can be cast or molded approximately to form and then finished by machin- 4'5 ing. ;In producing laps in these ways, any suitable lap material can beused. such as iron or the softer metal alloys; However, it is to be understood that I use the term lap in a broad sense including not only metal laps,

such as above referred to, which in use are adapted tohave abrasive material applied to their surfaces, but as well any rigid body presenting abrasive grains on its working surface and preferably, though not necessarily,

embedded therein, thus; including, for exobject of the invention is the the lapping of splined ample, bodies having abrasive surfaces made of abrasive grains held together by a binder.

.asvin the case of vitrified grinding wheels,

also natural abrasive stones, and the like. Obviously the term lap in the broad sense in which I employ it is inclusive of bones.

The lap having been formed, I support it and the object to be lapped with their complementary surfaces in abutting relation and then cause a rapid vibratorymovement of the two bodies relative to each other, said movement being of a nature to cause the complementary surface of said body and lap to slide upon each other with abrasive action, Obviously this can most readily be done by holding one of the bodies in fixed position and giving the other body the necessary vibratory movement.

- When the tooth surfaces of a gear, a bevel gear for example, are being lapped, my process includes the additional steps of setting up a mutual torsional pressure between the teeth of the gear and lap during their vibratory movement in relation to each other and intermittently indexing one relative to the other about their commonaxis.

In order that my process and apparatus suitable for carrying it out may be clearly understood in detail I will now describe preferred forms of apparatus shown in the accompanying drawings and then explain the manner in which the apparatus isremployed;

In the drawings,

Fig. l is a'front elevation of lapping apparatus adapted to lap bevell "'ears.

Fig. 2 is a vertical sectio n the broken line 2-2, Fig. 1.

Fig. 3 is a plan view of some of the upper parts of the machine.

Fig. 4 is a fragmentary horizontal section on the line,44, Fig. 2.

Fig. 15 is a horizontal 5"5, Fig. 2.

Fig. 6 is a fragmentary sectional view illustrating a detail of the construction.

Fig. 7 is a vertical sectional view of a somewhat modified form of machine adapted to shafts.

Fig. 8 1s a side view of a splined shaft of the type formed with a collar which closes the section on the line inter-spline spaces at one end.

Fig. 9 is an end view of said shaft.

Fig. 10 is a fragmentary front elevation showing some of the details of the mechanism.

Referring in detail to the construction illustrated in Figs. 1 to 6, inclusive, 1 designates the frame of the machine in its entirety, this frame comprising a base section 2 and ian upright section 3. The upper part of the frame is formed with a forwardly projecting arm 4 which isformed at its front end with a square or rectangular aperture 4 toslidably support a square or rectangular work support 5. 1

Near its upper end the work support 5 is formed with a slot 5 which extends from its front to its rear side. This slot is designed to accommodate an eccentric 6 which is mounted on a shaft 7 that, in turn, is carried by the forked front end of an arm 8 which is adj ustably mounted on the main frame. The work support 5 is also formed with a transverse slot in which is fitted an eccentric block 9 to engage the under side of the eccentric 6 and, above the eccentric, the Work support 5 is formed with a somewhat similar slot in upper side of the eccentric 6. The upper end of the work support 5 is fitted with two screws 11 which have a swivelling engagement at their lower ends with the block so that the latter can be adjusted vertically toward or from the lower block 9 to compensate for wear or to accommodate eccentrics of difierent sizes. I Lock nuts 12 serve to secure the adjusting screws 11 in position. The adjustable mounting of the arm 8 is effected by mounting its rear end on a transverse shaft 13 which is coupled at one end to an electric motor 14 suitably mounted on the main frame and is rotatably supported at its other end in a bearing 15 similarly supported on the main frame. The arm 8 is formed with a downwardly extending slotted extension 8 and the rigid arm 4 of the main frame has a stud bolt 16 which projects throughthe slot of the extension 8 and is fitted with a lock nut 17 by which the arm 8 can be clamped in any position to which it is adjusted about the shaft 13. To facilitate such adjustment, arm 4 is provided with a lug 4 in which is mounted an adjusting screw 18 that engages the lower end of the arm extension 8 so that the arm 8 can be readily adjusted up and down with considerable nicety. The shaft 7 is fitted with a pulley 7 and the shaft 13 with a pulley 13 and a belt 7 on these two pulleys serves to transmit power to the shaft 7 from the motor 14.

The lower end of the work support 5 is formed with a cylindrical extension 5 adapted to receive the hub of the gear or the like to be lapped. As illustrated a bevel gear a is shown, this gear being clamped to the work carrier by a nut on a threaded stud-20 in the lower end of the work support 5. With the bevel gear (1!. thus mounted it can be given a rapid vibratory axial movement by the rotation of the eccentric 6 which through its engagement with the blocks 9 and 10 reciprocates the work support 5 in the frame arm 4.

' Directly below the bevel gear a is a lap 21 which is formed with a circular series of teeth complementary in form to the teeth of the bevel gear a, the lap and gear being co axially disposed. The lap 21 is mounted on the upper end of a shaft 22 which is formed with a collar 22 on which the lap is sup ported and against which it is clamped by a nut and washer assembly 23 on stud bolt 24 that projects from the upper end of the shaft 22. Both the lap 21 and the gear a are secured against rotation on their respective supports by keys as illustrated.

The upright shaft 22 is slid-ably and r0 tatably mounted in a bearing sleeve 25 which in turn is rotatably supported in an arm 26 on the frame 1. A spline 27 between the shaft 22 and the sleeve 25 prevents their relative r0- tation while permitting their relative movement axially.

The lower end of shaft 22 is formed with a socket which rotatably engages a shaft 28 having an enlarged and forked lower end 28 carrying a transverse pin 29 on which is mounted a cam roller 30. The roller 30 engages a large cam wheel 31 mounted on a shaft 32 which has bearing supports 33 and 34 that are in turn bolted to the base 2 of the main frame. The bearing supports 33 and 34 are formed with upright slotted extensions 33 and 34, the slots of which are engaged by the respective ends of the pin 29 so that the latter is permitted to rise and fall but only in one plane so that the cam roller 30 is maintained in alignment with the cam wheel 31.

The cam shaft 32 and cam wheel 31 are driven by the following mechanism. On the shaft 32 is secured a worm wheel 35 which is driven by a worm 36 on a shaft 36 mounted in bearing supports 37, 38 and 39 on the main frame. The rear end of the shaft 36 carries a bevel gear 40 which meshes with a similar gear 41 on a shaft 42 mounted in frame bearlugs 43 and 44. The outer end of the shaft 42 carries a pulley 45 which is driven by belt 46 that passes over driving pulley 47 on the shaft 13. The cam shaft 32 is thus driven at much lower speed than the upper shaft 13.

The cam wheel 31 is circular throughout the major part of its length but at one point is formed with adepression 31 While the roller 30 is engaged with the circular part of the cam the lap 21 is sustained in working relation to the gear a to be lapped, but when, in the rotationof the cam wheel 31, the roller 30 travels downward into the depression 31, the lap 21 is lowered and disengaged from the gear a to permit indexing of the one in relation to the other.

This indexing last referred to is effected by the following means: A worm wheel 48 is keyed to the lower end of the sleeve or hollow Inn ' shaft and in mesh with this wheel is a worm 49 mounted on a shaft 50 rotatably mounted in bearing brackets 51, 51 and 52, 52, carried by the main frame of the machine. A skew gear 53 splined on one end of the shaft 50 meshes with a similar gear 54 which is mounted upon the upper end of a vertical,

shaft 55. The upper end of shaft 55 has a bearing support in the bracket 52 while its lower end is rotatably mounted in a bearing 56 which extends upward from the frame base 2. Near the bearing 56 is an upright boss 57 in which is secured a stud shaft 58. On the latter shaft is rotatably mounted a skew gear 59 and a plain spur gear 60 secured to the skew gear to turn therewith. The skew gear 59 is moved intermittently by gear wheel 61 fast on the adjacent end of the shaft 32, the gear wheel 61 having a single tooth 61 which engages. the teeth of the gear 59 to give the latter a short movement on each rotation of the shaft 32. This intermittent turning movement of the gear 59 is transmitted to the shaft 55 through the gear 60, an intermediate gear 62, and a gear 63 fast on the said shaft 55. The intermediate gear 62 is rotatably mounted on a stud shaft 64: carried by a supporting arm 65 that is clamped by a screw 66 to the stud shaft 58 so that said arm can be adjusted to different angular positions about the shaft-58 thus permitting the use of gears 60, 62 and 63 of difierent sizes and arrangements to vary the amount of the indexing movement transmitted from the shaft 32 to the hollow shaft or sleeve 25. It will of course be understood that the tooth 61 of the gear wheel 61 is so disposed an 'ularly in relation to the depression 31 of t e cam 31 that the train of gearing between the shafts 32 and 25 is actuatedonly when lowering and disengagement of the lap 21 has been effected by the rotation of the cam.

In order to effect a suitable pressure between the teeth of the gear a and the lap 21 during the relative vibration, means is provided to exert a torsional force on the lap, this being accomplished by exerting a yielding endwise pressure on the worm 419 which thus exerts a turning pressure on the worm wheel 48 in somewhat the same manner as a rack exerts the turning pressure on a plain spur gear. This yielding pressure tending to turn the worm wheel 48 thus causes a corresponding pressure between the sides of the lap teeth and the gear teeth with which they 3 The yielding endwise pressure on the worm 49 is effected b a rocker 67 which is mounted on a stud sha 68 projecting from the main frame 1. One arm 67 a of this rocker is in the form of a flat spring which engages a collar 69 on the worm shaft '50 while a rigid arm 67 of the rocker engages a lifter 70 which is mounted upon the lower end of the shaft 22 being supported by the enlargedend 28 of shaft 28. The relation engage on one side.

of the parts is such that when the. shaft 22 is raised by the cam 31 the lifter 70 engages the spline between the said shaft and the gear 53.

Also springs 50 are preferably provided to centralize the shaft 50 when not pressed end wise by the rocker 67 or 71 later referred to. The above-described endwise pressure of the worm, of course, is exerted through the worm wheel on only one side of the gear teeth and the lap teeth and in order to effect the lapping of the opposite sides of the gear teeth I provide a second rocker 71 which is similar to the rocker 67 and is adapted through its spring arm to engage a collar 72 on the shaft 50 and exert an endwise pressure thereon in the opposite direction from that exerted by the rocker 67; To actuate the rocker 71 it is only necessary to raise the lifter 7 0 somewhat and turn it 180 so that it will engage the rocker 71 and not the rocker 67, the lifter 70 being held in each op rative position by a tongue groove connectifin 73 with the enlarged lower end of the shaft 28.

The operation of the above machine in carrying out my improved process will now be readily understood. A suitable lap 21 having been prepared in any of the ways hereinbefore described, such lap is rigidly clamped upon the upper end of the shaft 22. Then, with the shaft 22 in its lower-most position, one ofthe gears, a, .to be lapped is similarly r clamped upon the lower end 5 of thework supporter, If the lap 21 is of the plain metal typewitlfout abrasive embedded in its surfaces, a suitable abrasive in a paste form is now brushed upon the teeth of the lap or of the gear or both. Next the motor 14 is started. The resulting rotation of the eccentric 6 causes a very rapid vibratory reciprocation of the work support 5 and the gear a mounted thereon. The amplitude of the vibratory movement thus given to the gear a is determined of course by the eccentricity of the eccentric 6 and accordingly the amplitude can be varied through a substantial range by simply substituting eccentrices of different eccentricity. The rotation of the motor shaft 13 is also transmitted to the gearing mounted on the base of the machine thus causing a rotation of the cam shaft 32. The resulting rotation of the cam 31 lifts the lap carrier 22 so as to bring the teeth of the lap into mesh with the teeth of the gear; a. During the lifting of the lap carrier 22 and after the teeth of the lap and gear have partially intermeshed the rocker 67 (or 71), is engaged i by the part 70 so as to set up a torsional pressure between the teeth of the lap and the gear.. When the lap has thus been lifted to its I full elevation it is there firmly held by the cam roller rolling upon the circular face of the cam "31' with the result that a lapping action between the teeth of the cam and the teeth of the gear, on one side of the teeth, is

set up and continued'throughout the greater part of the rotation of the cam 31, this lap- I ping action ceasing as the rotation of the cam ing to the circular pitch of the lap and gear.

moi; -y described and including worm Thereupon, as the rotation of the cam 31 continues, the lap 21 is again lifted into operative engagement with the gear a and the same cycle of operations is repeated. This may be continued until the desired truing of the teeth of the gear a has been effected and ordinarily, if a suitable speed of reciprocation of the work support 5 is provided, this will i be effected when the indexing of the lap has been carried through one complete revolution. In-this connection it is to be observed that the collars 69 and 7 2 can be adjusted on the shaft to vary the torsional pressure set up between the lap and the gear.

lVhen the teeth of the gear have thus been trued on one side the truing of the other side of the teeth is effected by simply adjusting the lifter device 70 through 180 so that torsion between the lap and gear is set up in the opposite direction.

When the truing of both sides of the gear .teeth has been completed the machine is stopped with the lap in lowered position, thus permitting removal of the gear a so that another can be put in its place for-lapping.

To further illustrate the application of my invention I have shown in Figs. 7 to 10 a modified form of machine which is adapted for the lapping of short splinedshafts such,

for example, as are often used in the power transmission line between the engine and the rear axle of automobiles. This modified form of construction is not illustrated in complete detail because in most respects the construction is entirely similar to that already described except for dimensional differences. /Vith this understanding it will suifice to briefly state that the machine comprises a main frame 75, vibratory work supporter 76, lap carrying shaft 7?, cam 78 for raising and lowering the lap and a train of gearing between the shaft of cam 7'8 and the lap carrier 7 designed to index the lap, this train of gearing being somewhat similar to that described construction rockers 81 and 82 serve junction with a stud bolt 84 which it engages.

This work clamp is designed to embrace the reduced end 6 of the splined shaft 6 which is tobe lapped. This splined shaft, it will be observed on reference to Fig. 8, is formed 'with' a collarb and consequently the interspline spaces are closed at one end.

' The lap 85 which is designed to be used in lapping the spline shaft is in the form of a cup-shaped body formed with internal teeth complementary to the teeth or inter-spline spaces of the spline shaft. The lap is formed with an aperture at its lower end so that it can be clamped upon the upper end of the work carrier as-is clearly shown.

In carrying out In process as applied to the lapping of the sp ine shaft by the use of the machine shownin Fig. 7, the procedure is precisely the same as that described in connection with the first form of construction and it will accordingly be understood without further description. However, it is to be noted that in the lapping of the spline shaft the conditions differ in one notable respect from the conditions in the lapping of the bevel gear. In the latter case' the amplitude of the vibration given'to the gear should be minimized because it is desirable that the different parts of the tooth surfaces of the 'gear be rubbed only by the corresponding.

parts of the tooth surfaces of the lap. In the case of the spline shaft, on the other hand, there is no such limitation and the amplitude of the vibration may be made as large as may be desired or as may be convenient in all other respects in order to secure the desired results. In my improved vibratory lapping, the. minimum amplitude of vibration maybe considered to be the diameter of the grain of the abrasive employed. However, I consider that a suitable vibratory movement for the lapping of bevel gears such as ate-employed in the rear axles of automobiles is from 0.010" to 0.0207 though possibly the movement might satisfactorily be made as little as 0.005 and as great as 0.030".

The process constituting the subjectof the present invention is in part similar in principle to the process set forth in the earlier ap' plication of myselfand Maxwell I. Mathewson, Serial No. 551,141, filed April 10, 1922.

That is to say, in the present invention just as ML 7 J3 J5 4.1

titty tu the uJu A. i 5113121885 ()1 e116 gear gears,

or shaft andhave the same diametral and circular pitches. Again, in-the present invention just' as in the earlier one, the lap and gear are relatively indexed sothat each tooth of the lap may be brought successively into lapping engagement with each tooth of the gear with the resulting averaging, and there-- fore equalizing, of the spacing of the teeth of the gear and with the resulting averaging of the form or profile ofthe teeth of the gear.

Thus, in the present process just as in the earlier process the gear teeth are spaced with a very high-degree of accuracy and they are shaped with a close approximation to the true or theoretical tooth contour or profile, assuming that the gear, tostart with, has a fair approximation to the true tooth form such as is readily attainable with commercial gear cutting methods. At the same time the tooth surfaces are given the exceedingly smooth finish characteristic of lapping, just as in the earlier process described. The present process has'still a further point in common with the earlier process in that it tends automatically to secure concentricity of the'pitch circle of the gear with the gear axis with a minimum of lapping. This result is due to the fact that when the torsional pressure is set up between the lap and the, toothed or splined body being lapped the two bodies tend to ad-' just themselves to a position of concentricity with a common axis. This may be permitted in the apparatus illustrated by the slight play of the lap supporting shaft in its supporting bearings. The present process, however, differs markedly in certain other respects from the earlier process referred to. The

earlier process included long, relatively slow reciprocating strokes of the lap relative to the gear with indexing between each stroke. It is of course quite impossible in this manner to effect the lapping of a bevelled gear, or of a shrouded spur gear or of a splinedishaft with a collar,'because the closing oif of the inter-teeth spaces in all these cases as wellas the disposition of the teeth in relation to the gear axis in the case of beveLgears makes the long stroke of the earlier process quite impossible. The extremely short vibration of the present process, on the other hand,

overcomes' the difliculty incident to the dis position of the teeth relative to the gear axis in the case of bevel gears and by roviding a large number of rapid short stro es between each indexing movement I attain the necessary lapping effect reasonably rapidly so that in spite of the very short vibratory move,- ments which are necessary in-the case of bevel for example, the abrasive or lapping action is sufficiently rapid to make the proc-v ess economically feasible.

It is to be understood that the applications of the process and the forms of apparatus disclosed are presented simply as typical instances and byway of explanation of and that the carrying out of the process and the embodiment of the apparatus can be varied widely within the bounds of the appended claims.

What I claim is:

1. The method of lapping bodies having a circular series. of regularl {spaced teeth or projections with their lntertooth spaces closed by surfaces transverse to the axis of said circular series, which method comprises forming a lap with surfaces complementary to the -teeth surfaces to be lapped; supporting the toothed body and lap coaxially with their mutually complementary surfaces in? abutting relation; causing a rapid vibratory axial movement of the body and lap relative-to each other while maintaining the said abutting relationship between the complementary surfaces; meanwhile setting up a mutual torsional pressure betweenthe teeth of the body and lap; and intermittently disengaging the teeth of the body and lap by relative axial movement and progressively indexing one angularlyrelative to the other about their common axis.

2. The method of lapping bodies having a circular series of regularly spaced teeth or projections with their intertooth spaces closed by surfaces transverse to the axis of saidcircular series, which method comprises forming a lap with surfaces complementary to the teeth surfaces to be lapped; supporting the toothed body and lap coaxially with their mutually complementary surfaces in abutting relation; causing a rapid vibratory axial movement of the body and lap relative to each other'while maintaining the said abutting relationship between the complementary surfaces; meanwhile setting up a mutual torsional pressure between the teeth of the body and lap and maintaining a suitable abrasive between the complementary surfaces; and intermittently disengagin the teeth of the body and lap by relative axial movement and progressively indexing one angularly relative to the other about their common axis. .e

8. The method of lapping bevel gears which comprises forming a lap with surfaces .compfementary to those of the gear teeth to be lapped; supporting the gear and lap coaxially with their mutually complementary surfaces in abutting relation; causing a short and rapid vibratory axial movement of the gear and the lap relative to each other wh1 le maintaining the said abutting relationship between the complementary surfaces; meanwhile setting up a mutual torsional pressure between the teeth of the gear and lap; and intermittently disengaging the gear and lap by relative axial movement and progressively indexing one relative to the otherabout their which comprises forming a lap withsur aces complementary to those of the gear teeth to be lapped; supporting the gear and lap coaxially with their mutually complementary surfaces in abutting relation; causing a short and rapid vibratory axial movement of the gear and the lap relative to each other while maintaining the said abutting relationship between the complementary surfaces; meanwhile setting up a mutual torsional pressure between the teeth of the gear and lap and maintaining a suitable abrasive between the complementary surfaces; and intermittently disengaging the gear and lap by relative axial movement and progressively indexing one relative tothe other about their common axis.

5. The method of lapping which comprises forming a lap with surfaces complementary to those of the body to be lapped; supporting the said body and lap with their mutually complementary surfaces in abutting relation; causing a rapid vibratory movement of an amplitude less than 0.030 of an inch of the two bodies relative to each other in a manner effecting acorresponding relative sliding of the complementary surfaces on each other while maintaining the said abutting relationship; and meanwhile maintaining a suitable abrasive between the said complemenlary surfaces.

6. The method of lapping bodies having a circular series of regularly spaced teeth with their inter-tooth spaces closed by surfaces transverse to the axis of said circular series, which method comprises forming a lap with surfaces complementary to the teeth surfaces to be lapped; supporting the toothed body and lap coaxially with their mutually complementary surfaces in abutting relation; causing a rapid vibratory axial movement of an amplitude less than 0.030 of an inch of the body and lap relative to each other while maintaining the said abutting relationship between the complementary surfaces; meanwhile setting up a mutual torsional pressure between the teeth of the'body and lap; and intermittently disengaging the teeth of the body and lap by relative axial movement and progressively indexing one angularly relative to the other about their common axis.

7. The method of lapping beveled gears which comprises forming a lap with surfaces complementary to those of the gear teeth to be lapped; supporting the gear and lap coaxially with their mutually complementary surfaces in abutting relation; causing'a rapid vibratory axial movement of an amplitude less than 0.030 of an inch of the gear and the lap relative to each other while maintaining the said abutting relationship between the complementary surfaces; meanwhile setting up a mutual torsional pressure between the teeth of the gear and lap; and intermittently disengaging the gear and lap by relative axial movement and progressively indexing one relative to the other about their common axis.

8. In apparatus for lapping bodies having a circular series of regularly spaced teeth or projections, the combination of supporting means for a body to be lapped; a body formed with a circular series of lapping teeth complcmentary to those of the body to be lapped; means for supporting the lap coaxially with the body to be lapped with their complementary teeth in abutting relation; means for causing a rapid vibratory axial movement of the bodies relative to each other while maintaining the said abutting relationship; means for setting up a. mutual torsional pressure between the teeth of the two bodies during said vibratory movement; means for intermittently moving one of the bodies out of and into engagement with the other; and means for indexing one of the bodies angularly relative to the other while they are out of engagement.

9. In apparatus for lapping bodies, the combination of a support for the body to be lapped; a lapping body formed with surfaces complementary to those of the body to be lapped; means for operatively supporting the lap with its lapping surfaces abutting the complementary surfaces of the body to be lapped; and means for causing a rapid vibratory movement of an amplitude less than 0.030 of an inch of one of the'bodies relative to the other in a manner effecting a corresponding relative sliding of the complementary surfaces on each other while maintaining the said abutting relationship of said surfaces. 1

In testimony whereof, I hereunto aflix my signature.

ALEXANDER W. COPLAND. 

